Antislip sheet material with twisted tapes

ABSTRACT

A sheet of material suitable for roofing or industrial wrapping applications has an anti-skid surface formed by ridges of twisted tapes. The sheet comprises a woven scrim of warp tapes and weft tapes. Some of the tapes are twisted about their longitudinal axis, for example about (25) to (400) revolutions per meter, to form ridges having a height substantially greater than the thickness of the tapes. The ridges impart an anti-skid surface to the sheet. The scrim is bonded to a coating or film to make the sheet waterproof.

RELATED APPLICATIONS

This application is a divisional application of U.S. Ser. No. 12/740,908filed on Apr. 30, 2010, titled ANTISLIP SHEET MATERIAL WITH TWISTEDTAPES, which is the is the U.S. national phase entry of PCT/CA08/01938,with an international filing date of Nov. 5, 2008, which claims thebenefit of U.S. Provisional Patent Application No. 60/985,604, filed onNov. 5, 2007, the entire disclosures of which are incorporated herein byreference.

TECHNICAL FIELD OF THE INVENTION

The invention pertains to sheet materials made of plastic tapes,suitable for roofing, wrapping and other applications. Moreparticularly, it pertains to such sheet materials having a surface witha high coefficient of friction.

BACKGROUND OF THE INVENTION

Sheet materials comprising a scrim of woven plastic tapes are commonlyused for roofing and industrial wrapping applications. The sheetmaterials may be coated or uncoated. Such materials typically have arelatively smooth surface with a low coefficient of friction. For someapplications, it is useful for the sheet material to have antislipproperties. For example, if the sheet is to be applied to a roof deck,e.g. as a roofing underlayment, a surface with antislip properties onwhich workers may walk enhances worker safety. Likewise, if the sheetmaterial is to be use to wrap goods such as bundles of lumber, on whichworkers may need to walk, an antislip surface is useful. Theconventional methods of imparting antislip properties to sheet materialsinvolve applying films, meshes or granules to the surface of the sheet.

SUMMARY OF THE INVENTION

The invention provides a sheet material comprising a scrim made of wovenplastic tapes, in which at least some of the tapes

comprising the scrim are twisted to create ridges and thus impart anenhanced coefficient of friction to a surface of the sheet. The sheetmaterial provides enhanced slip-resistance in wet, dry or dustyconditions. The sheet material is useful for applications such asindustrial wrapping, packaging and roofing underlayments.

The invention provides a sheet of material having an anti-skid surface,comprising a first set of tapes generally parallel to each other and asecond set of tapes generally parallel to each other and perpendicularto the first set of tapes. The tapes are plastic and have a widthgreater than their thickness. The tapes of the first set and of thesecond set are interwoven with each other to form a scrim. At least someof the tapes of the first set are twisted about their longitudinal axisto form a plurality of parallel ridges having a height at least fivetimes greater than the thickness of untwisted tapes, the ridges formingthe anti-skid surface of the sheet.

According to another embodiment of the invention, there is provided asheet of material having an anti-skid surface comprising a first set oftapes generally parallel to each other, a second set of tapes generallyparallel to each other and perpendicular to the first set of tapes, anda third set of tapes generally parallel to the first set of tapes. Thetapes are plastic and have a width greater than their thickness. Thetapes of the first set and of the third set are interwoven with thetapes of the second set to form a scrim. At least some of the tapes ofthe third set are twisted about their longitudinal axis to form aplurality of parallel ridges having a height at least five times greaterthan the thickness of untwisted tapes, the ridges forming the anti-skidsurface of the sheet. Each tape of the first set is positioned adjacentto and following a weaving path the same as that of a respective tape ofthe first set.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of a sheet according to a first embodiment of theinvention.

FIG. 2 is a cross-sectional view on the line 2-2 of FIG. 1.

FIG. 3 a cross-sectional view of a second embodiment of the invention.

FIG. 4 is a cross-sectional view of a third embodiment of the invention.

FIG. 5 is a plan view of a fourth embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Exemplary embodiments are illustrated in the referenced figures of thedrawings. It is intended that the embodiments are to be consideredillustrative rather than restrictive.

Referring to FIGS. 1 and 2, the sheet material 10 has a scrim 12 coatedon one side by a coating layer 14. The scrim 12 is woven in a plainweave of warp tapes 16 and weft tapes 18. The weft tapes 18 are laidflat in the weave, in the conventional manner. The warp tapes 16 aretwisted, such that they describe full revolutions about theirlongitudinal axis along the length of the weave. The frequency of thetwisting is about one revolution every centimeter. Preferred frequenciesof such twisting are in the range of 25 to 400 revolutions per meter.Some of the twisted tapes can have different frequencies of twistingfrom others.

The thickness of the tapes comprising the scrim is about 1 to 2 mils(0.025 to 0.05 mm). However, when twisted, the effective thickness ofthe warp tapes 16 is about 10 to 20 mils (0.25 to 0.5 mm). The warptapes 16 accordingly form ridges, having a height of about 10 to 20mils, running along the warp direction of the sheet 10, which provide anincreased coefficient of friction to the surface of the sheet. To forman effective anti-skid surface, the height of the ridges should be atleast about five times greater than the thickness of the tapes,alternatively at least about ten times greater.

The scrim 12 and the coating 14 are made of plastic, poly olefin resins,for example polyethylene or polypropylene. They may alternatively bemade of various other plastics, including polyesters, polystyrene, nylonand ethylene acrylic copolymers. Alternatively, the scrim and/or thecoating 14 may comprise a high coefficient-of-friction material, forexample ethylene vinyl acetate (EVA), ethylene methyl acrylate (EMA),rubber or elastomer. The scrim provides a structural layer having hightensile and tear strength.

The tapes 16, 18 are conventional extruded plastic tapes having a flatprofile and a width greater than their thickness. The tape width ispreferably about 1.5 to 6 mm. The number of tapes per inch in themachine direction and in the cross direction is in the range of 1 to 25.Tapes that are to be twisted may be the same width and thickness astapes that are not to be twisted, or they may have a greater widthand/or thickness.

The frequency of twisting of the warp tape 16, and the thickness anddenier of the tapes 16, 18 can be selected to achieve the desiredcoefficient of friction of the anti-skid surface of the sheet 10.

The coating layer 14 is a waterproof film bonded to the scrim. It may bepermeable to water vapor to allow the escape of moisture from buildingswhen the sheet is used as a roofing underlayment or for similarapplications. The coating layer 14 is manufactured in-situ using aco-extrusion process and is laminated to the scrim 12, or it cancomprise a film that is bonded to the scrim, for example by thermalbonding, lamination or adhesive. Optionally, a second coating layer isbonded to the opposite side of the scrim.

FIG. 3 illustrates an embodiment of the invention in which twisted warptapes are added to a scrim woven with conventional untwisted warp andweft tapes. The sheet material 20 comprises a scrim 22 with a coatinglayer 14 laminated thereto. The scrim 22 is woven of untwisted warptapes 21 and untwisted weft tapes 23 in a plain weave. Twisted warptapes 25 are woven into this scrim, the twisted warp tapes 25 being laidon top of and following the same weaving path as the untwisted warptapes 21, interweaving with the weft tapes 23 of the scrim. The twistedwarp tapes 25 form a twisted warp layer 24. This layer 24 comprisesridges formed by the twisted warp tapes 25, imparting an enhancedcoefficient of friction to the upper surface of the sheet 20.

FIG. 4 illustrates a further embodiment of the invention in which bothtwisted warp tapes and twisted weft tapes are added to a scrim wovenwith conventional untwisted warp and weft tapes. The sheet material 30comprises a scrim 22 with a coating layer 14 laminated thereto. Thescrim 22 is woven of untwisted warp tapes 21 and untwisted weft tapes 23in a plain weave. Twisted warp tapes 25 and twisted weft tapes 27 arewoven into this, the twisted warp tapes being laid on top of andfollowing the same path as the untwisted warp tapes 21, and the twistedweft tapes 27 being laid on top of and following the same weaving pathas the untwisted weft tapes 23. The twisted warp tapes 25 and twistedweft tapes 27 form a layer 26 which comprises ridges formed by thetwisted warp tapes and twisted weft tapes, imparting an enhancedcoefficient of friction to the upper surface of the sheet 30.

FIG. 5 illustrates a further embodiment of the invention in which thesheet material 40 comprises a scrim 50 with a coating layer 14 (notshown) laminated thereto. The scrim 50 includes twisted warp tapes 42and twisted weft tapes 44, and untwisted warp tapes 46 and untwistedweft tapes 48. The twisted warp tapes replace every fourth untwistedwarp tape, and the twisted weft tapes replace every third untwisted wefttape, in the example shown. Alternatively, the twisted tapes may beplaced at different intervals, for example replacing every wrap and/orweft tape, or every second or every fifth, etc. warp and/or weft tape.

In the sheet materials of the invention, either or both of the warp andweft tapes can be twisted; and the sheet material can be uncoated,coated on one side or on both sides; and it can include additionallayers, depending on the properties desired for a particularapplication.

Some further features and embodiments of the invention include thefollowing:

(a) The weft tapes are twisted and the warp tapes are untwisted;

(b) Both the warp tapes and the weft tapes are twisted;

(c) Each warp (and/or weft) tape is twisted, or every second or thirdetc. warp (and/or weft) tape is twisted and the others are untwisted;

(d) Where twisted tapes are added to a scrim made of untwisted tapes (asin FIGS. 3 and 4) the added twisted tapes may be in the machinedirection or in the cross direction or both;

(e) The scrim is uncoated, or coated on one side, or coated on bothsides, or includes additional layers;

(f) The weave of the scrim is plain, twill or other weaves;

(g) The color of the twisted tapes is the same as the surrounding fabricto blend in with it; or it is different to make the antislip grid morevisible;

(h) The twisted tapes are applied to the whole of a sheet or to only apart of it;

(i) Adjacent twisted tapes have different frequencies of turning, forexample some have relatively more and some have relatively fewerrevolutions per meter, creating a rougher surface with ridges ofdifferent heights;

(j) The twisted tapes or the coating, or both, are treated with orcomprise a tacky or high coefficient-of-friction coating or additive.For example, they may incorporate ethylene vinyl acetate (EVA), ethylenemethyl acrylate (EMA), rubber or elastomer; and/or

(k) The sheet material includes additives or is treated to provideUV-resistance.

Although the invention has been described in terms of variousembodiments, it is not intended that the invention be limited to theseembodiments. Various modifications within the scope of the inventionwill be apparent to those skilled in the art. The scope of the inventionis defined by the claims that follow.

The invention claimed is:
 1. A roofing underlayment having an anti-skidsurface, the roofing underlayment comprising: a first set of tapesgenerally parallel to each other; and a second set of tapes generallyparallel to each other and perpendicular to the first set of tapes;wherein tapes of the first set and tapes of the second set are plasticand have a width greater than their thickness; wherein the tapes of thefirst set are interwoven with the tapes of the second set to form ascrim; wherein every fourth tape of the first set is twisted betweenabout 250 revolutions per meter and about 400 revolutions per meterabout its longitudinal axis to form a first plurality of spaced apartparallel ridges; wherein every third tape of the second set is twistedbetween about 250 revolutions per meter and about 400 revolutions permeter about its longitudinal axis to form a second plurality of spacedapart parallel ridges; wherein the first plurality of spaced apartparallel ridges and the second plurality of spaced apart parallel ridgesform an anti-skid contour of the anti-skid surface of the sheet.
 2. Theroofing underlayment of claim 1, further comprising a waterproof film onthe scrim.
 3. The roofing underlayment of claim 1, further comprising afilm bonded to the scrim by lamination, wherein said film comprises ahigh coefficient of friction elastomer.
 4. The roofing underlayment ofclaim 1, further comprising a first extrusion coating on a first side ofthe scrim and a second extrusion coating on a second side of the scrim.5. The roofing underlayment of claim 1, wherein twisted tapes of thefirst set have the same width as other tapes of the first set.
 6. Theroofing underlayment of claim 1, wherein twisted tapes of the second sethave different widths than other tapes of the second set.
 7. The roofingunderlayment of claim 1, wherein the tapes of the first set and thetapes of the second set have a tape width of between about 1.5 mm andabout 6 mm.
 8. The roofing underlayment of claim 1, wherein each of thefirst set of tapes and the second set of tapes have between about 1 tapeper inch and about 25 tapes per inch.
 9. The roofing underlayment ofclaim 1, wherein ridges of the first plurality of spaced apart parallelridges and ridges of the second plurality of spaced apart parallelridges have a height at least five times greater than a thickness ofuntwisted tapes of the first set and untwisted tapes of the second set.10. The roofing underlayment of claim 1, wherein ridges of the firstplurality of spaced apart parallel ridges have a height of between aboutten mils and about twenty mils.
 11. The roofing underlayment of claim 1,wherein each twisted tape of the first set are laid on top of and followa same weaving path of an untwisted tape of the first set.
 12. A roofingunderlayment having an anti-skid surface, the roofing underlaymentcomprising: a first repeating pattern of tapes comprising flat tapes andtwisted tapes, wherein the tapes of the first repeating pattern aregenerally parallel to each other, wherein the twisted tapes of the firstrepeating pattern are twisted between about 250 revolutions per meterand about 400 revolutions per meter; a second repeating pattern of tapescomprising flat tapes and twisted tapes, wherein the tapes of the secondrepeating pattern are generally parallel to each other, wherein thetwisted tapes of the second repeating pattern are twisted between about250 revolutions per meter and about 400 revolutions per meter; whereinthe tapes of the first repeating pattern are interwoven with the tapesof the second repeating pattern to form a scrim, wherein the tapes ofthe first repeating pattern are generally perpendicular to the tapes ofthe second repeating pattern; wherein the twisted tapes of the firstrepeating pattern and the twisted tapes of the second repeating patternform an anti-skid contour of the anti-skid surface of the sheet.
 13. Theroofing underlayment of claim 12, wherein each of the twisted tapes ofthe first repeating pattern and the second repeating pattern are twistedinto a circular cross-section.
 14. The roofing underlayment of claim 12,further comprising an extrusion coating on the scrim.
 15. The roofingunderlayment of claim 12, wherein the twisted tapes of the firstrepeating pattern have the same width as the flat tapes of the firstrepeating pattern.
 16. The roofing underlayment of claim 12, wherein thetwisted tapes of the second repeating pattern have different widths thanthe flat tapes of the second repeating pattern.
 17. The roofingunderlayment of claim 12, wherein the tapes of the first repeatingpattern and the tapes of the second repeating pattern have a tape widthbetween about 1.5 mm and about 6 mm.
 18. The roofing underlayment ofclaim 12, wherein each of the first repeating pattern and the secondrepeating pattern have between about 1 tape per inch and about 25 tapesper inch.
 19. The roofing underlayment of claim 12, wherein the twistedtapes of the first repeating pattern and the twisted tapes of the secondrepeating pattern form ridges having a height at least five timesgreater than a thickness of the flat tapes of the first repeatingpattern and the flat tapes of the second repeating pattern.
 20. Theroofing underlayment of claim 12, wherein the twisted tapes of the firstrepeating pattern and the twisted tapes of the second repeating patternform ridges having a height between about ten mils and about twentymils.
 21. The roofing underlayment of claim 12, wherein the twistedtapes of the first repeating pattern are laid on top of and follow asame weaving path of the flat tapes of the first repeating pattern, andwherein the twisted tapes of the second repeating pattern are laid ontop of and follow a same weaving path of the flat tapes of the secondrepeating pattern.
 22. The roofing underlayment of claim 1, wherein eachof the twisted tapes of the first set and the second set are twistedinto a circular cross-section.